The present invention relates in general to the bag making art, and is more particularly concerned with a new and improved method of and means for providing extruded thermoplastic reclosable fastener means, commonly referred to as zipper, for bags which may be formed from plastic film and provided with mouth ends closable by means of the zipper.
As heretofore generally provided, the zippers have either been extruded integrally with the bag making film, or the zippers may have been preformed in continuous strip and supplied in rolls for subsequent use in a bag making line. This is exemplified in recently issued U.S. Pat. No. 4,835,835.
An inherent disadvantage of the continuous rolling of thermoplastic zipper is the distortion that develops due to the memory of the winding system. This manifests itself as memory of the spool known as curvature and camber which causes deviation from a straight line. It may be noted, however, that in the accepted mode of applying zipper to substrates in packaging machines, the zipper is kept under tension in order to minimize the difficulty in application of the zipper to the substrate. In cases where zero deviation from straightness is required, the zipper must be held under extreme tension. In applications where the zipper cannot be held under tension, application of the zipper to a substrate is virtually unattainable.
The provision of sectional lengths of zipper to be applied to the outside of bags is disclosed in U.S. Pat. No. 4,691,373. In that disclosure, pressure sensitive adhesive is provided on the predetermined length of zipper and a peelable protective strip is applied over the pressure sensitive adhesive until the sectional length of zipper is to be used. That disclosure does not meet the problem of supplying predetermined lengths of zipper in a ready availability mode for applying separate lengths of the zipper to bags in a bag production line, especially as conducted in a bag making machine.